(1) Field of the Invention
The present invention relates to an aircraft airfoil, and to an aircraft having such an airfoil. More particularly, the invention relates to a stabilizer, and in particular to a stabilizer for an aircraft having a rotary wing.
(2) Description of Related Art
A stabilizer is a stationary airfoil that is generally located at the rear of an aircraft fuselage. Under such circumstances, a stabilizer is specifically designed to develop forces suitable for stabilizing and/or controlling pitching movements of the aircraft, and possibly also movements in yaw of the aircraft.
A stabilizer may comprise a set of substantially horizontal airfoils and of substantially vertical airfoils.
The substantially horizontal airfoils serve in particular to optimize the stability of the pitching movement of the aircraft. Such substantially horizontal airfoils are conventionally referred to as a “tail plane” or a “horizontal tail”. It should be observed that a horizontal stabilizer may include a movable portion referred to as an “elevator”.
A horizontal stabilizer may pass through an aircraft fuselage and extend on either side of the fuselage, or indeed it may extend from only one side of the fuselage. A horizontal stabilizer extending on either side of a fuselage may comprise a single airfoil passing through the fuselage or two airfoils extending from the fuselage in two respective opposite directions.
Independently of the way the horizontal stabilizer is made, the horizontal stabilizer includes a system for fastening it to the fuselage.
Substantially vertical airfoils serve in particular to optimize the stability of the roll movement of the aircraft. Such substantially vertical airfoils are conventionally referred to as a “tail fin”. A tail fin may include a movable portion referred to as a “rudder”.
Thus, an aircraft conventionally has an airfoil provided with a system for passing it to a fuselage, such as a stabilizer.
Furthermore, such a member of an aircraft that projects from the fuselage runs the risk of being impacted in flight by an obstacle, such as a bird. A stabilizer may be the subject of a risk of bird impact when the stabilizer projects by a non-negligible amount outwards from the aircraft.
Damage to a stabilizer as a result of a bird impact can have an influence on safety in flight, so manufacturers tend to optimize stabilizers against impacts of this kind.
More particularly, a bird impact runs the risk of breaking the fastener system connecting an airfoil to an aircraft fuselage, since an impact against a bird generates excessive forces on the fastener system.
Conventionally, an airfoil comprises a main structure around a spar. The airfoil is also provided at its leading edge with a protective front structure.
The terms “main structure” and “front structure” are used below for convenience and for reasons of clarity.
For example, the front structure is fastened to a spar of the airfoil by ribs.
Under such circumstances, when a bird impacts the front structure, the front structure deforms without stopping the bird. The bird penetrates into the inside of the stabilizer and then impacts against the spar of the airfoil.
By definition the spar is very strong. The spar therefore does not deform under the impact. However the spar moves back and pivots about the fastener system for the airfoil.
The fastener system becomes deformed and, in the extreme, it may break.
In order to minimize the risks of an impact, a first device is known that is used in particular on a cover of a tail gearbox of the helicopter known under the trademark EC175®.
That first device makes use of a blade fastened to the outside of the front structure of the cover. The blade is intended to cut through a bird, should that be necessary in order to protect the cover, and more particularly in order to protect its fastener system connecting it to the body of the aircraft.
That first device gives satisfaction. However the blade disturbs the aerodynamic flow of air around the cover.
In addition, the cover is reinforced in order to enable the blade to be fastened thereto. Since the front structure is generally dimensioned in order to withstand light external loading, the front structure needs to be modified in order to receive the blade.
The resulting stiffening of the front structure tends to give rise to a non-negligible increase in its weight.
Furthermore, fabrication of the stabilizer is made more complex.
A second device is known and described in document EP 2 196 391.
That second device consists in reinforcing the front structure of an airfoil. The reinforcement may be obtained by means of chemical machining or indeed by adding Y-shaped reinforcement. The purpose of the second device is thus to maximize the amount of energy that the front structure absorbs as a result of impacting against a bird.
That second device is also satisfactory. Nevertheless, reinforcing the front structure gives rise to a significant increase in the weight of the airfoil. In addition, the fabrication of that airfoil and more particularly of its front structure is made more complex.
The first device thus suggests modifying the front structure by adding a blade, while the second device suggests modifying the front structure by reinforcing it.
Also known is document U.S. Pat. No. 7,931,233. That document relates to a protective skin forming a leading edge.
The technological background also includes the document “Wing leading edge design with composites to meet bird design strike requirements”, Composites Manufacturing, Butterworth Scientific, Guildford, Surrey, GB, Jan. 1, 1991, pp. 3-18.
The technological background also includes the following documents: U.S. Pat. No. 2,390,761; US 2010/148007; EP 2 130 762; and DE 10 2005 060958.